Determination of Nitrogen/Protein in Cheese (FP928)

Importance of the Topic

Protein content is a key nutritional and economic parameter in cheese. Rapid and precise measurement of total protein supports quality control, nutritional labeling, and economic valuation in dairy production.

Objectives and Overview of the Study

This application note presents a method for determining total nitrogen and calculated protein in various cheese types using the LECO FP928 combustion analyzer. The study evaluates performance with different carrier gases and sample gas aliquot loops to demonstrate precision, accuracy, and throughput.

Methodology and Used Instrumentation

The method is based on Dumas combustion in a high temperature ceramic furnace under pure oxygen. Combustion gases pass through a reduction tube to convert NOx to N2 and then into a thermal conductivity detector for nitrogen measurement. Key steps include

• Sample preparation to ensure uniform consistency
• Use of ceramic combustion boats and an autoloader for automated analysis
• Selection of 3 cm3 or 10 cm3 aliquot loop size to balance precision and reagent life
• Carrier gas choice of helium for highest sensitivity or argon for cost efficiency

Used Instrumentation

• LECO FP928 macro combustion nitrogen determinator
• Ceramic combustion boats
• Thermal conductivity detector
• Primary filter tube with glass and steel wool
• Autoloader arm

Reference Materials

• LECO Certified Reference Materials and other suitable standards
• ISO 14891 modified for data generation

Main Results and Discussion

Typical analyses of Parmesan, Swiss, Pepperjack and Cheddar cheese produced consistent nitrogen and protein values with relative standard deviations below 0.1 percent. Key observations include

• Helium as carrier gas yielded higher sensitivity and lower detection limits compared to argon
• 10 cm3 loop provided optimal precision in the low nitrogen range
• 3 cm3 loop extended reagent life with minimal performance impact
• Average protein values matched expected ranges: Parmesan ~30 percent, Swiss ~19 percent, Pepperjack ~24 percent, Cheddar ~22.5 percent

Benefits and Practical Applications

This combustion method eliminates hazardous reagents and lengthy sample digestion. Analysis time is approximately five minutes per sample. Advantages include

• High throughput suitable for routine quality control
• Minimal sample preparation
• Automated calibration and drift correction procedures
• Applicability to nutritional labeling, process control, and economic assessment

Future Trends and Opportunities

Emerging developments may include

• Integration with online monitoring systems for continuous production control
• Expansion to other dairy and food matrices
• Advanced data analytics for real time quality assurance
• Alternative carrier gas options and miniaturized detection modules

Conclusion

The LECO FP928 Dumas combustion analyzer delivers rapid, accurate, and precise nitrogen and protein determination in cheese. Its automation and flexibility make it an effective tool for dairy laboratories and production facilities.

Reference

ISO 14891 Milk and Milk Products Determination of Nitrogen Content by Combustion Dumas Principle